Butterfly valves normally consist of a housing or body within which an annular elastomeric seat is mounted for the purpose of effecting a resilient seal against the valve closure member. The valve closure member is a disc which may be rotated from an open position aligned with the direction of flow of a fluid through the valve to a closed position at right angles to the direction of flow. In this latter position, the peripheral edge of the disc tightly engages the valve seat to effect a seal. In the conventional butterfly valve, this seat is molded of an elastomeric material whereby, as the valve's disc is rotated into closed position, the seat has a limited degree of resilience which will permit a seal effecting interference fit between the disc and the seat, providing a fluid tight closure.
The need for a certain degree of resilience and, thus, displacability of the valve seat necessitates the use of an elastomeric material. Materials of this type have a tendency to creep or migrate when subjected to high pressure, particularly when the pressure is applied to the seat on one side of the disc without a corresponding supporting pressure on the other side of the disc. The need to control this migration or creep without sacrifice of the necessary resilience of the elastomeric material has caused the industry to adopt the use of reinforcing members in the seat. These reinforcing members are rigid and provide support for the elastomeric material, limiting its ability to creep or migrate.
One of the more commonly used types of reinforcement is an annular ring or band of rigid material embedded within the seat as the seat is molded. It is important that this reinforcement be accurately positioned within the seat if the seat is to have uniformity of strength and accurate control of deflection, migration and creep is to be maintained. During the actual molding process, the elastomeric material is injected into the mold, at high pressures. These tend to not only deflect but also displace the reinforcement member and, thus, mislocate it within the seat. This results in a defective seat. This invention overcomes this problem.
One proposal for solving this problem is disclosed in U.S. Pat. No. 3,537,683 issued Nov. 3, 1970 to A. H. Snell, Jr., entitled VALVE SEAT FOR A BUTTERFLY VALVE AND METHOD FOR MAKING THE SAME. This solution, however, is not entirely satisfactory. It results in openings in the valve seat which extend from the outer periphery of the valve seat through the reinforcement member, thus, creating a weakness which, as the patent points out, will result in leakage under certain circumstances. If this result is to be avoided, the opening has to be subsequently plugged to prevent the leakage. Even plugging does not overcome the fact that an opening is created through the reinforcement member, thus, permitting differential deflection of the seat at the hole because the plug cannot provide the same uniformity of support as would a continuous, uninterrupted reinforcement member. Further, this solution requires providing two additional holes through the reinforcmeent member before it is placed in the mold. These holes must be accurately indexed both to the holes for the shaft openings and to the locator pins in the mold used to index the reinforcement member during molding. This invention provides a solution to this problem which eliminates the necessity for thus maintaining such accuracy.
This invention has the further advantage of so molding the seat that the holes that result from the reinforcement member indexing pins extend axially into the seat from the ends of the seat terminating at the edge of the reinforcement member. Thus, they are never located beneath the point of sealing contact of the seat and the valve disc when the valve disc is closed. Further, they hold the reinforcement ring by clamping the edges of the ring, thus requiring no modification of the reinforcement ring. Since they are located in the end faces of the sealing member, they can be positioned between the end sealing beads. As so located, they are completely sealed from the entry of fluids which might otherwise enter from either the interior or the exterior of the valve, depending upon whether the valve is being used in a line which is operating under elevated or sub-atmospheric pressures.